Tkinter variable.get() don't work with different window

Question

I have 2 windows, in both I create some Entry. In the first window the method .get() take the text that I wrote but when I call the the second window and write in the Entry the .get() don't work. I append the code of the second window:

TableData = tk.Tk()
canvas4 = tk.Canvas(TableData, width=480, height=120, bg='lightsteelblue2', relief='raised')
canvas4.pack()
labelT = tk.Label(TableData, text='Dati Tabella', bg='lightsteelblue2')
labelT.config(font=('helvetica', 20, 'bold'))
canvas4.create_window(240, 60, window=labelT)

frameT = Frame(TableData)
frameT.pack()

NomeFile = StringVar()
DataEsame = StringVar()
CodFiscale = StringVar()

TableFrame1 = LabelFrame(frameT)
TableFrame1.config(font=('helvetica', 20, 'bold'))
TableFrame1.grid(row=1, column=0)

lblFileName = Label(TableFrame1, text='Nome file:', font=('helvetica', 20, 'bold'))
lblFileName.grid(row=0, column=0)
txtFileName = Entry(TableFrame1, font=('helvetica', 20, 'bold'), textvariable=NomeFile)
txtFileName.grid(row=0, column=1)

lblData = Label(TableFrame1, text='Data esame:', font=('helvetica', 20, 'bold'))
lblData.grid(row=1, column=0)
txtData = Entry(TableFrame1, font=('helvetica', 20, 'bold'), textvariable=DataEsame)
txtData.grid(row=1, column=1)

lblCodF = Label(TableFrame1, text='Cod Fiscale:', font=('helvetica', 20, 'bold'))
lblCodF.grid(row=2, column=0)
txtCodF = Entry(TableFrame1, font=('helvetica', 20, 'bold'), textvariable=CodFiscale)
txtCodF.grid(row=2, column=1)

def getDataTab(event):
    global mydb

    file_name = (NomeFile.get())
    data_db = (DataEsame.get())
    codF = (CodFiscale.get())
    print(data_db)
    print(file_name)
    print(codF)
    TableData.destroy()

TableData.bind('<Return>', getDataTab)
TableData.mainloop()

The code of the first window is the same but with different names for the variables and the tkinter objects. When I print the 3 variable that I get They are void.